The thermal transfer printing technique has been generally known as an art of softening a thermally fusible ink on an ink sheet by a thermal head, and directly transferring and recording on an exclusive image receiving medium such as thermal transfer paper. Other recording technique is recently reported, in which a thermally fusible ink is transferred once on a drum- or belt-shaped intermediate recording medium of which surface is made of silicone rubber or the like, and this ink is transferred again on a paper. This; technique is proposed to solve the problems experienced in the general thermal transfer recording technique without using intermediate recording medium in which it was difficult to print and record at high quality without voids or other defects on plain paper or bond paper other than thermal transfer paper. This method is capable of recording uniformly because of the homogeneity and flexibility of the silicone rubber, and transferring and fixing the ink recorded on the rubber, smoothly along surface irregularities of the paper owing to the flexibility of rubber. The silicone rubber used herein is fabricated in a hardness range of 30 to 50.sup.HS by using, for example, dimethly silicone, and copolymerizing and crosslinking with methyl butyl silicone, and adding inorganic filler such as silicon.
In the thermal transfer recording method using the intermediate recording medium with the surface covered with silicone rubber stated above, it is possible to print and record at high quality on a plain paper. Generally, the silicone rubber formed in a drum shape is required to possess properties of ink receptivity when recording, and ink releasability when transferring. However, when the drum-shaped silicone rubber intermediate recording medium is used continuously, the releasability of the rubber surface deteriorates, and the ink on the silicone rubber is not completely transferred onto paper or other image receiving medium, and is left over on the rubber surface, thereby impairing the image quality. It is conceivable that the deterioration in ink releasability is attributable to the increase of roughness of rubber surface due to friction against the paper, or to the decrease of oil quantity in the rubber, when silicone oil is added to the silicone rubber in order to improve the releasability, due to the transfer of the silicone oil to the paper. Because of these reasons, in the conventional thermal recording method using intermediate recording medium made of silicone rubber and thermally fusible ink, the number of transfers by the intermediate recording medium was limited to about several thousand times. Besides, the thermally fusible ink used in such method is required to be easily adhered on a material very low in surface energy such as silicone rubber when forming an image, and, to the contrary, to be completely transferred to the paper without being left over on the intermediate recording medium at the time of transfer. However, the existing thermal transfer recording ink is designed to be transferred directly on the material having a high ink receptivity such as paper, and when the ink was used in the indirect thermal recording method by using the intermediate recording medium, recording on silicone rubber and transferring on paper could not be satisfied at the same time.